The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the inventors hereof, to the extent the work is described in this background section, as well as aspects of the description that does not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted to be prior art against the present disclosure.
An analog-to-digital converter (ADC) is an electronic component that converts an analog signal into a digital signal. For example, a sound collected by a microphone or light captured by a digital camera is received in the form of an analog signal, and is converted into a digital signal by the ADC for processing. The analog signal is usually passed through a driving circuit, such as a filter, a programmable amplifier (PGA) or a transimpedance amplifier (TIA) before being fed into the ADC.
The ADC usually includes one or more latched comparators, which generate a digital output indicating whether a differential analog input signal is positive or negative. A switch is usually used in the latched comparator to operate the latched comparator in different phases. When a switching event takes place, the resulting voltage variation within the comparator can be coupled to the input of the comparator through parasitic capacitances of the transistors within the comparator. As the driving circuit preceding the ADC usually has a non-zero output impedance, the input signal of the ADC is disturbed and such disturbance is usually referred to as the kickback noise.
In a switch cap input ADC, a large value of capacitor array can be switched at the same time, the resulting kickback noise may be non-negligible and thus may affect the input and reference voltages of the ADC, which impairs the accuracy of the ADC. To avoid the kickback noise being fed into the ADC, sometimes the driving circuit preceding the ADC is designed to absorb the kickback noise. Redesigning driving circuit may impose burden to circuit engineers if every driving circuit preceding every ADC needs to be redesigned. Also, a redesigned driving circuit that is configured to absorb kickback noise may require more circuit area and power.